Restadolescent sleep timingTeens · General

A teenager's late night is partly biology, not defiance.

Research on adolescent biology finds a natural shift in the body's internal clock during the teen years — meaning early starts fight against biology, not just habit.

Study title: Teenage Sleep Patterns Actually Shift Later — Crowley, S. J., Wolfson, A. R., Tarokh, L., & Carskadon, M. A., Journal of Adolescence, 2015

Study type: Systematic review
Population: Adolescents, multiple studies across countries
Published: 2015
Evidence confidence: Strong confidence

The short version

During adolescence the internal body clock shifts later: melatonin is released later in the evening than in childhood or adulthood, which makes early sleepiness genuinely harder to reach. Early school start times then cut the night short at the other end.

Why it matters

It changes the conversation at home from willpower to scheduling — and makes the wind-down hour worth protecting when the start time can't move.

The question

How does the timing of the body's internal clock change during adolescence, and what does that mean for sleep patterns and school schedules?

How it was studied

A review of research on circadian and sleep-need changes across puberty, drawing on studies measuring melatonin timing, sleep-wake patterns, and school-schedule outcomes in teenagers.

What they found

During adolescence, the body's internal clock shifts later — melatonin is released later in the evening than in childhood or adulthood — making early natural sleepiness harder to achieve, while early school start times cut sleep short on the other end.

Limitations

Individual variation in circadian shift timing is large, most direct physiological measurements come from smaller lab-based studies, and social/behavioural factors like screen use interact with the biological shift in ways that are hard to fully separate.

What it may mean

Struggling to fall asleep early and struggling to wake up early during the teen years isn't purely about habits or discipline — there's a real biological shift in sleep timing during this stage of life.

In real life

This is part of why 'just go to bed earlier' often doesn't work as advice — the body isn't ready for sleep yet, even if the clock says it should be.

Try this

Where possible, protect the sleep you can control — consistent wind-down, dim light before bed — since the total sleep window is already fighting against biology.

Evidence confidence

Strong confidence

The circadian phase-delay finding in adolescence is well replicated across sleep science; specific numeric estimates and individual variation are less precise.

Source

Crowley, S. J., Wolfson, A. R., Tarokh, L., & Carskadon, M. A. (2015). Teenage Sleep Patterns Actually Shift Later. Journal of Adolescence.

Peer-reviewed · Full text may be paywalled · Last reviewed 2026-08-15

Read the original research →

One study isn't the whole storyOne study gives us a piece of the picture. Selfey looks for patterns across the broader evidence rather than treating a single finding as a rule.

Read this in everyday terms

You Don't Have to Earn Rest

Selfey research briefs are educational summaries, not medical advice, diagnosis or treatment. Research describes patterns across groups; it cannot tell you what is right for your situation.

Related research

Turn the evidence into a plan you can actually carry out.

Check in →